1. Field of the Invention
The present invention relates to a television signal receiving tuner, and more particularly to an input circuit unit for a television signal receiving tuner in the U.S. specification, which is utilized for use on a vehicle and/or for used in a personal computer, and which is also adapted to receive Frequency Modulation (FM) broadcasting signals.
2. Description of the Related Art
A conventional television signal receiving tuner in the U.S. specification (hereinafter, it is simply referred to as a tuner) will be described with reference to FIGS. 4 and 5. FIG. 4 shows an input circuit unit for a conventional tuner, and FIG. 5 shows a selectivity characteristic for a part of the input circuit unit shown in FIG. 4. First, in FIG. 4, a VHF input circuit unit is constituted such that an induction-M high-pass filter 53 in a parallel type, a constant-K high-pass filter 54, an induction-M high-pass filter 55 in a serial type, a shunt trap 56, and a VHF input tuning circuit 57 are connected in series sequentially between an input terminal 51 and a VHF high-frequency amplifier 52. Also, a UHF input circuit unit 58 including a UHF input tuning circuit (not shown), etc. is connected to the input terminal 51.
The induction-M high-pass filter 53 in the parallel type is constituted of a first inductor 59 and a first capacitor 60 connected in parallel each other, and a shunt inductor 61, the respective one ends of the first inductor 59 and the first capacitor 60 are connected to the input terminal 51, and the other ends thereof are grounded through the shunt inductor 61. Further, a cut off frequency of this induction-M high-pass filter 53 in the parallel type is set to approximately 54 MHz, and the parallel resonance frequency by the first inductor 59 and the first capacitor 60 is set to approximately 41 MHz.
Moreover, the constant-K high-pass filter 54 is constituted of a shunt inductor 61 and a series capacitor 62 in which one end thereof is connected to the one end of this shunt inductor 61, and a cut off frequency thereof is also set to approximately 54 MHz. Accordingly, it leads to the shunt inductor 61 being commonly used by the induction-M high-pass filter 53 in the parallel type and the constant-K high-pass filter 54.
The induction-M high-pass filter 55 in the serial type is constituted of a series capacitor 62, a second inductor 63 and a second capacitor 64, which are connected in serial each other, which are connected between the other end of this series capacitor 62 and the ground, and a cut off frequency thereof is set to approximately 54 MHz, and also a serial resonance frequency of the second inductor 63 and the second capacitor 64 is set to approximately 26 MHz.
Furthermore, the shunt trap 56 is constituted of a third inductor 65 and a third capacitor 66 which are connected in parallel each other, and a parallel resonance frequency by the second inductor 65 and the second capacitor 66 is set to approximately 46 MHz.
Then, by the induction-M high-pass filter 53 in the parallel type, the constant-K high-pass filter 54, the induction-M high-pass filter 55 in the serial type, and the shunt trap 56, as shown in FIG. 5, passing through a frequency band equal to or more than approximately 54 MHz as well as attenuating sharply with a frequency equal to or less than 54 MHz, in particular, the attenuations in the middle frequency band of a television (approximately 41 MHz to 46 MHz in the U.S. specification), and in the citizen band (26 MHz) to be used in a transceiver are made larger as equal to or more than 55 dB. As a result, it is arranged that an interference signal of in the middle frequency band of the television and an interference signal in the citizen band are not to be inputted into the VHF input tuning circuit 57, and the VHF high-frequency amplifier 52, etc.
The VHF input tuning circuit 57 is constituted of four tuning inductors 67, 68, 69, 70 and a varactor diode 71, and is arranged such that a tuning frequency thereof can be varied by varying a capacitance value of the varactor diode 71. In this VHF input tuning circuit 57, the tuning inductors 67, 68, 69 and the varactor diode 71 are connected in a pai-shape, and one end of the tuning inductor 67 is grounded with a direct current blocking capacitor 72, and an anode of the varactor diode 71 is also grounded. A connecting point of the tuning inductor 67 and the tuning inductor 68 is connected to the shunt trap 56 through the direct current blocking capacitor 73 and the coupling inductor 74 being in series, and a connecting point of the tuning inductor 69 and a cathode of the varactor diode 71 is connected to the VHF high-frequency amplifier 52 through the coupling capacitor 75. Further, it is arranged such that the tuning inductor 70 is connected in parallel to the tuning inductor 67, through switch diodes 76, 77 respectively connected to the respective both ends thereof.
Further, the respective anodes of switch diodes 76, 77 are connected to a high-band switch terminal 79 through a resistor 78, and the respective cathodes thereof are connected to a low-band switch terminal 81 through a resistor 80, and moreover, the other terminal (cathode) of the varactor diode 71 is connected to a tuning voltage terminal 83 through a tuning inductor 69, a resistor 82.
Then, when receiving the television signals of the high-band, the switch diodes 76, 77 are set in the conducting state by applying a high-band switch voltage to the high-band switch terminal 79 (at this time a low-band switch voltage is not applied to the low-band switch terminal 81), and the tuning inductor 67 and the tuning inductor 70 are connected in parallel as high-frequency wise, thereby a tuning frequency of the VHF input tuning circuit 57 is made higher. Further, when receiving the television signals of the low-band, the switch diodes 76, 77 are set in the non-conducting state by applying a low-band switch voltage to the low-band switch terminal 81 (at this time a high-band switch voltage is not applied to the high-band switch terminal 79), and the tuning inductor 70 is being separated from the tuning inductor 67 as high-frequency wise, thereby a tuning frequency of the VHF input tuning circuit 57 is made lower. Then, a capacitance value of the varactor diode 71 is varied by a tuning voltage from the tuning voltage terminal 83, thereby it turns to be a tunable for the frequencies of the television signals of the respective channels in the low-band and the high-band which are allocated to the frequencies equal to or more than 54 MHz.
Further, although they are not shown, but a hybrid circuit, a local oscillator, etc. are connected to a post VHF high-frequency amplifier. Then, the television signals output from the VHF high-frequency amplifier 52 are frequency-converted to a middle frequency in the hybrid circuit.
Such a conventional tuner is incorporated into a car navigation system, for example, when utilizing as for use on a vehicle, but it was not enabling to receive the FM broadcasting. Therefore, it needs to incorporate an extra FM receiver or FM tuner and the like for receiving the FM broadcasting, and thus the car navigation system is turned to be complex, thereby a planning of the miniaturization and the lower price could not be made.
Furthermore, recently, a tuner is mounted on a personal computer, and it is considered that on a display thereof a picture (video) of a television is shown, or characters of a teletext are displayed, but in a conventional tuner the FM broadcasting could not be received, thereby the characters of the teletext in the FM broadcasting could not displayed.
Accordingly, it is an object of the present invention to provide a television signal receiving tuner which is capable of easily receiving the FM broadcasting signals, and also which is adapted to be not affected by other interference signals at a time when receiving the television signals or the FM broadcasting signals.
In order to solve the above problem, a television signal receiving tuner of the present invention comprises
a first input terminal to which a television signal is input;
a second input terminal to which a FM broadcasting signal is input;
a VHF input tuning circuit;
a television signal input circuit provided between the first input terminal and the VHF input tuning circuit for passing through a television signal; and
a FM broadcasting signal input circuit provided between the second input terminal and the VHF input tuning circuit for passing through a FM broadcasting signal,
wherein, the FM broadcasting signal input circuit and the VHF input tuning circuit is to be separated in high frequency wise at a time of receiving the television signal, and
wherein, the television signal input circuit and the VHF input tuning circuit is to be separated in high frequency wise at a time of receiving the FM broadcasting signal.
The television signal receiving tuner of the present invention comprises:
a first switch diode provided between the television signal input circuit and the VHF input tuning circuit; and
a second switch diode provided between the FM broadcasting signal input circuit and the VHF input tuning circuit,
wherein, the first switch diode is brought into conduction, and the television signal having passed through the television signal input circuit is input into the VHF input tuning circuit through the first switch diode, as well as the FM broadcasting signal input circuit and the television signal input circuit are separated in high frequency wise at a time of receiving the television signal,
wherein, the second switch diode is brought into conduction, and the FM broadcasting signal having passed through the FM broadcasting signal input circuit is input into the VHF input tuning circuit through the second switch diode, as well as the first switch diode is brought out of conduction, and the television signal input circuit and the VHF input tuning circuit are separated in high frequency wise at a time of receiving the FM broadcasting signal.
The television signal receiving tuner of the present invention is arranged that the television signal input circuit comprises at least a first intermediate frequency trap for attenuating an intermediate frequency band of the television, in which a first inductor and a first capacitor are connected in parallel each other, and the FM broadcasting signal input circuit comprises at least a highpass filter for attenuating a frequency less than a FM broadcasting frequency band.
The television signal receiving tuner of the present invention is arranged that a cathode of the first switch diode and a cathode of the second switch diode are connected to the ground in direct current wise through a common resistor,
a television switch voltage for switching to a receiving state of a television signal is applied to an anode of the first switch diode when receiving the television signal, and
a FM switch voltage for switching to a receiving state of a FM broadcasting signal is applied to an anode of the second switch diode when receiving the FM broadcasting signal.
The television signal receiving tuner of the present invention is arranged that the FM broadcasting signal input circuit further comprises a serial trap connected between a signal path and the ground, in which a second inductor and a second capacitor are connected in series each other, and wherein a trap frequency of the serial trap is set to a frequency band in the low-band of a television broadcasting.
The television signal receiving tuner of the present invention comprises a second intermediate frequency trap for attenuating an intermediate frequency band of the television, in which a third inductor and a third capacitor are connected in parallel each other, between a connection point of the cathode of first switch diode and the cathode of second switch diode and the VHF input tuning circuit.